1. Field of the Invention
The present invention relates to plasma generators, and more particularly to devices having a nozzle that discharges a plasma plume.
2. Discussion of the Related Art
In recent years, the progress on producing plasma by use of microwave energy has been increasing. Typically, a plasma producing system includes a device for generating microwave energy and a nozzle that receives the microwave energy to excite gas flowing through the nozzle into plasma. One of the difficulties in operating a conventional plasma producing system is providing an optimum condition for plasma ignition—a transition from the gas into the plasma. Several parameters, such as gas pressure, gas composition, nozzle geometry, nozzle impedance, material properties of nozzle components, intensity of microwave energy applied to the nozzle, and distance between the nozzle exit and the portion in the nozzle where the microwave energy is focused, for instance, may affect the plasma ignition condition. The threshold intensity of the microwave energy for plasma ignition can be reduced if the nozzle impedance can be adjusted to its optimum value so that the amount of microwave energy received by the nozzle can be maximized. Thus, there is a need for a nozzle that has a mechanism for adjusting the nozzle impedance.